Emission tomography is a field of medical diagnostic science in which a radiation detector is used for obtaining an image of the radiation distribution from a radioisotope within the body of a patient. A conventional computer program can use the received data to produce a "picture" in two dimensions of the radiation distribution of a section through a patient. Usually, the radioisotope is ingested into the patient either orally or by injection and is of the type that concentrates in the area of the body to be investigated. For example, certain isotopes tend to concentrate in a tumor, and certain isotopes concentrate in particular body parts (e.g. iodine isotopes concentrate in the thyroid gland). Once the isotopes are concentrated, the radioisotope detector is used to detect the radiation at various points about the body and then a computer is utilized to generate two dimensions depictions of the radiation concentration aligned along a selected axis at various points on that axis.
In order to detect the radiation at the various points, it is necessary to move the patient relative to the detector. Two Anger U.S. Pat. Nos. 3,432,660 and 3,011,057 disclose an early type of radiation image detector and a tomography carousel in which the patient moves relative to the detector.
However, in more recent emission tomography apparatuses, including gamma radiation camera SPECT systems, the scintillation camera head, or radioisotope detector, rotates around a patient positioned on a separate patient support. Several U.S. patents disclose tomography devices in which the detector orbits the patient. They include the Perusek et al U.S. Pat. No. 4,651,007 (disclosing an apparatus capable of circular and noncircular orbits with individual positioning of the detector and of the patient support table); and the Fujiki U.S. Pat. No. 4,698,506 and Barfod U.S. Pat. No. 4,652,758 (disclosing devices in which patient support is positionable with respect to an orbiting detector.
Any system in which the detector moves will suffer form undesirable detector motion and image degradation resulting from such motion. In addition, such detectors have an extremely high density and typically weigh 1 to 2 tons. Therefore maintaining the accuracy during the rotational motion requires an extremely expensive support and motion control systems. Nevertheless, such systems still suffer from a lack of concentricity and angular locatability. The other disadvantages of such systems are their high cost, huge size and mechanical repair problems. As the result of the cost and size, there are relatively few medical institutions that can afford to obtain and use the conventional, commercially available SPECT systems. Consequently, the highly diagnostic SPECT procedures are unavailable for a significantly large number of medical institutions.
One reason why the medical diagnostic apparatuses developed from the concept of a stationary detector disclosed in the aforementioned Anger patents to that of the movable detector disclosed in the other aforementioned patents is the lack of proper patient support provided in the former devices. Without such support, patient movement will add greatly to the inaccuracies thereof. Several U.S. patents disclose patient supports usable with radiation equipment. These patents include the Saussereau U.S. Pat. No. 4,779,858; the O'Dell et al U.S. Pat. No. 4,400,820; the Larsson U.S. Pat. No. 4,481,657; and the Urgan et al U.S. Pat. No. 4,674,107. Many of these patents merely disclose a patient table that has provision for immobilizing the patient and which is simply positionable relative to a radiation detector or radiation source.
There is therefore the need for an emission tomography carousel usable to perform SPECT which is relatively inexpensive, requires a minimal amount of space, is sturdy yet accurately positionable, and which is versatile in use for the various body organs that can be investigated.